Why is my battery percentage always either 100% or 0%?

My iPod's battery percentage is really weird. When it runs out of juice it turns off. After 5 hours of charging, it's fine, but the battery percentage is 0%. After 5-10 min of using (without charging), the percentage becomes 100%, and after another 30 min-1 hour the percentage becomes a number between 70 and 90. Within another 30 min-1 hour the percentage becomes 0%, then after 5 min, the iPod turns off. I know this really seems long and repetitive, but my main point is that I want my battery percentage to be accurate.

Please answer! Thanks a lot!